L0301P74 - Cellular and Tissue Response
Cells *normally maintain a steady state (homeostasis) *active participants in their environment *respond or adapt to changes - stresses/stimuli in their environment Consequences of Cell Injury *reversible: if injury is within the limit where cells can still return to a stable baseline  —> tissue regeneration or adaptation *irreversible: if stress or injury is severe, persistent and rapid in onset, cell injury is irreversible  —> tissue repair Cellular Adaptations *physiological **usually in response to normal stimuli ***hormones **endogenous chemical medication *pathological **cells modify structure and function in response to stress **considered an abnormal adaptation  Principle Adaptive Responses *hypertrophy: increased cell size = increased organ size *hyperplasia: increased cell numbers *atrophy: decreased cell size = decreased organ size *metaplasia: change in cell morphology (but can be reversible if not too severe) *if adaptability is exceeded or stress is too severe —> cell death Causes of Cell Injury *oxygen deprivation **often caused by blood clots *chemical agents *infectious agents *immunological reactions *genetic factors *nutritional imbalances **e.g. calcium imbalance, deficiency of vitamins, unbalanced diet *physical agents **e.g. motor vehicle accidents, burns *ageing Examples of Injuries MRI of the Thigh: Observations - age 63: *more white, less grey and more dispersed Analysis - age 63: *reduced muscle mass *increased fat *thinner bone - osteoporosis Neurological Tissue Injury *extensive trauma *radiation *congenital defect *alcohol *genetic disease *Alzheimers disease Capacity for Tissue Regeneration *labile **cells continuously proliferate and able to repair **e.g. skin *stable **normally replicate infrequently but can be respond when necessary **e.g. haematological cells, liver (to an extent) *permanent **normally do not replicate or regenerate **e.g. neurological tissue, retina Factors Influencing Tissue Response *amount of damage: **size / volume of tissue injured *type of tissue involved **capacity of cells in tissue to regenerate *duration of the injury **length of time that injury persists **particularly with oxygen deprivation (stroke, blood clot) Labile Tissue Example: Skin *epithelium of the skin **layers of flattened cells able to regenerate **regeneration occurs in the basal layers and “push upwards” to restore the top *abrasion **layer of fibrin (scab) **replacement of epithelial cells form underneath **skin restored to normal **new skin - lighter and pink due to lack of exposure to the environment Stable Tissue Example: Liver *quite susceptible to damage **from alcohol, drugs, ischaemia, chemicals *stable cell population **epithelium hepatocytes *excellent regenerative capacity *loss of scattered cells or small groups **regeneration *if damage is severe and affects the tissue architecture **repair with fibrous tissue - which are not capable of the original function and may lead to death of the organ Normal Liver *epithelial hepatocytes arranged in rows radiating out from a central vein with spaces in between *allows for filtration Cirrhosis of Liver *increase in amount of fat *buildup of connective tissue fibrin *regeneration is no longer possible *noduled and lumpy in appearance Permanent Tissue Example:  Cardiac Muscle *cardiac muscle cells lack the capacity to regenerate *damage —> repair with fibrous tissue *possible damage by myocardial infarction **ischaemia - blood has been cut off causing damage **time and location in the heart which is without blood will indicate the amount of damage **fibrous tissue is not capable of contracting like usual cardiac muscle therefore the part of the heart is compromised Possible Outcomes of Cell/Tissue Injury *regeneration **restoration of normal tissue *adaptation **growth of changed/adapted cells **most common: metaplasia *repair **death of cells and growth of different cells to the normal tissue **capacity of the organ to function is impaired